aplite

Aplite (/ˈæplaɪt/) is an intrusive igneous rock in which the mineral composition is the same as granite, but in which the grains are much finer, under 1 mm across.[1] Quartz and feldspar are the dominant minerals. The term 'aplite' or 'aplitic' is often used as a textural term to describe veins of quartz and feldspar with a fine to medium-grain "sugary" texture. Aplites are usually very fine-grained, white, grey or pinkish, and their constituents are visible only with the help of a magnifying lens. Dykes and veins of aplite are commonly observed traversing granitic bodies; they occur also, though less frequently, in syenites, diorites, quartz-diabases and gabbros https://en.wikipedia.org/wiki/Aplite